The addition of relatively hazardous chemicals to a swimming pool water is a standard operation for maintenance of the cleanliness and sanitation of the pool water. Various chemicals are used to maintain the condition of the swimming pool water. One such chemical which is widely used is chlorine, frequently in tablet form, and various other solid chemical compounds which upon dissolving provide chlorine or a chlorine containing composition. Other widely used additive chemicals for swimming pool water are algaecides and bacteriacides, which include various quaternary ammonium compounds. The use of these chemicals in swimming pools to control bacteria and the growth of algae and to maintain purity is well known. Because these chemicals, especially chlorine in the gaseous form, is toxic and hazardous to store and to handle, and because liquid chlorine is heavy and expensive to transport and store and also has a very limited storage life, and because granular chlorine such as the calcium hypochlorite variety is not completely soluble and introduces a cloudiness of high mineral content into the water other forms of chlorine supplying materials have been tried. One such material is tablet trichloro-isocyanurate which upon dissolution yields 80-90% chlorine. This material can be fed through a pool skimmer or a feeder of a kind which floats on the pool surface or by means of an automatic chlorinator that is connected, either directly or indirectly, to a pool filtration system.
The problem with known, existing devices aimed at the automatic dissolution and feeding of solid chemicals to swimming pool water is that most such devices have little, if any, control over the eroding rate of the solid chemical. The chemical, once wetted for the purpose of dissolving it, continues in contact with the dissolving liquid even when it is desired for whatever reason to stop further feed of the dissolving solid chemical. As a result, the concentration, of the solid chemical sitting in the dissolving liquid that is being fed becomes disproportionate. Also, often times, the efficacy of the solid chemical such as the chlorine supplying tablets remaining continuously in water contained in the chlorinated devices may have an adverse effect on the chemical. An important consideration in the maintenance of swimming pool water also resides in the timing and proportioning of the chemicals added. For example, when the swimming pool water quality has deteriorated to substantially, it then becomes necessary to introduce relatively disproportionately high amounts of chemicals in an effort to restore the quality and purity of the water. This results in higher cost because chemicals are wasted and in inconvenience in that the pool is unavailable for swimming. It is also recognized in the art that when a combination of chemicals in the optimum proportions is added at the proper time, lesser quantities of the chemical(s) are needed and the quality of the water is maintained uniformly and at a superior level. Studies have shown, for example, that when a timely addition is made of a small quantity of a quaternary ammonium algaecide with the chlorine additive it can result in a reduction of as much as 65 percent in the chlorine requirements. Reference, page 7 of the Buckman Laboratories, Inc., Memphis, Tenn. catalog on algae control in swimming pools, hot tubs, and spas (1/92). Also, prior art devices generally require loading of the chemical into the chlorinator by hand, thus resulting in potential injury to the hands as well as to the lungs of the user. One known device uses a canister devised to avoid such problems but the chemical to be fed is open to the atmosphere and vents gases resulting in corrosion to surrounding materials and vegetation.
It is accordingly apparent that a need exists for an improved reliable and efficient dispensing apparatus which is capable of introducing in a timely manner a combination of chemicals automatically in measured amounts and in the desired predetermined relative proportions into a liquid stream and in particular to the recirculating water stream of a swimming pool.